T3 //75 



L(, 



DEPARTMENT OF COMMERCE 



Technologic Papers 

OF THE 

Bureau of Standards 



S. W. STRATTON, Director 



No. 189 

METHOD FOR DIFFERENTIATING AND 

ESTIMATING UNBLEACHED SULPHITE 

AND SULPHATE PULPS IN PAPER 



R. E. LOFTON, Associate Physicist 
M. F. MERRITT, Laboratory Assistant 

Bureau of Standards 



APRIL 4, 1921 



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A METHOD FOR DIFFERENTIATING AND ESTIMATING 
UNBLEACHED SULPHITE AND SULPHATE PULPS IN 
PAPER 

By R. E. Lofton and M. F. Merritt 



ABSTRACT 

The purpose of this paper is to fill a need felt especially by paper chemists and ana- 
lysts for a rapid and reliable method of distinguishing between and of making an ap- 
proximately correct quantitative determination of mixtures of unbleached sulphite 
and sulphate pulps. This paper gives briefly the basic differences in the manufactiu'e 
of the two pulps, and contains a concise review of the methods that have been recom- 
mended from time to time for distinguishing between unbleached sulphite and sul- 
phate pulps. It gives the procediu-e followed in developing a new and comparatively 
rapid method for distinguishing between these pulps, and also gives some of the more 
important experiments carried out with various stains diuing this investigation. The 
method of preparing the new stain and the method of procedure for differentiating be- 
tween luibleached sulphite and sulphate fibers is described in detail, and tables show- 
ing the results of quantitative microscopical analysis of mixtiu-es of these fibers stained 
by the new method are given. 

CONTENTS 

Page 

I. Introduction 3 

II. Theoretical considerations involved 4 

1 . Fundamental differences between the two pulps 4 

2 . Possible bases of differentiation 5 

3. Different affinities of pulps for dyes 6 

III. Methods proposed by earlier experimenters 6 

1 . Klemm 's methods 7 

2. Schwalbe's methods g 

3. Fannon's methods 10 

IV. The malachite-green and fuchsine method 10 

1 . Soitfces of materials used 10 

2. Method of attack and earlier experiments 11 

3. Detailed method of using 12 

4. Estimating percentages 14 

V. Summary of results 15 

I. INTRODUCTION 

The purpose of this pubHcation is to give a review of the various 
methods proposed for distinguishing between unbleached sulphite 
and sulphate fibers, and especially to describe the development 
and application of a new method for accomplishing this result. 

3 



7'^-^ 



4 Technologic Papers of the Bureau of Standards 

That there is and has existed for some time a demand for a quick 
and certain method for differentiating between these two pulps is 
indicated by the various attempts that have been made from time 
to time to develop such a method. To be satisfactory, any method 
proposed must be practical as well as certain — that is, it must not 
require any expensive apparatus, or special experience, or tedious 
and lengthy manipulation- — but it must be such as may be carried 
out in a few minutes time by any one ordinarily familiar with the 
microscopical examination of paper-making fibers. 

Such a method would be of service to pulp manufacturers and 
jobbers, to manufacturers of sulphite and sulphate papers, and to 
the retailers and consumers of sulphite and sulphate papers in aid- 
ing them to determine whether they are getting what they desire. 
It is useless for a jobber or a consumer to specifically order an all 
or part sulphate wrapping paper unless there is some means of de- 
termining whether the article ordered is being furnished. 

The authors acknowledge the assistance of M. B. Shaw, who 
made a large number of fiber estimations, the results of which ap- 
pear in Tables 3,4, and 5, and who gave assistance as to methods 
of preparing the stains. 

II. THEORETICAL CONSIDERATIONS INVOLVED 
1. FUNDAMENTAL DIFFERENCES BETWEEN THE TWO PULPS 

The difficulties to be overcome in developing a method for dis- 
tinguishing between unbleached sulphite and sulphate pulps are 
due to the similarity of the pulps. Both are made, for the most 
part, from the same raw material, with but two or three exceptions. 
Spruce, hemlock, balsam fir, yellow pine, tamarack, and white fir 
are used in making both pulps. In addition to these woods, jack 
pine and cypress are often used in the sulphate process. Yellow 
pine is more generally used in the sulphate than in the sulphite 
process, because the former process is better adapted to woods rich 
in rosin and oil. The woods generally used in foreign countries 
are of the same kinds as those used in the United States and Canada 
except that black spruce is frequently used in Finland, Norway, 
and Sweden. 

Since the raw material from which these pulps are made is in 
general the same, the only distinguishable differences between the 
pulps are to be found in the two different digesting processes em- 
ployed in their manufacture. 

Sulphite pulp is made by cooking wood chips in a solution of 
bisulphite of calcium, or of calcium and magnesium. This solution 



Differentiating Unbleached Sulphite and Sulphite Pulps 5 

has an acid reaction. The chips are cooked under a steam pressure 
of from 60 to 80 pounds for from 8 to 20 hours. The process was 
invented by B. C. Tilghman, of Philadelphia, who took out the 
first United States patent in 1867. 

Sulphate pulp, frequently called "Kraft" (a German word 
meaning "strength"), is made by cooking wood chips in a solu- 
tion the chief ingredient of which is sodium sulphide. The sodium 
"sulphate" added from time to time is reduced to "sulphide" 
during the preparation of the cooking Uquor. The reaction of 
this solution is alkaline. In this process the chips are cooked 
imder a steam pressure of about 100 pounds for from 2 to 7 hours. 
This process was invented by Carl F. Dahl, of Danzig, Germany, 
about 1883, and was introduced into America in 1907, when the 
Brompton Pulp and Paper Co. set up a sulphate mill in Canada. 

Unbleached sulphite pulp is used in the manufacttue of wrapping 
paper and bag stock, of many so-called Kraft and manila papers, 
of twines used in tying bundles and in making paper rugs, onion 
and potato sacks, and in any pulp or paper product where strength 
is the chief consideration. Sulphate pulp has a considerably 
darker color than sulphite, for which reason the latter is often 
colored in the process of being made into paper to resemble sulphate 
pulp. In general, sulphate pulp may be used wherever it is per- 
missible to use unbleached sulphite. In cases where the greatest 
possible strength is required, sulphate is used instead of sulphite, 
since it is somewhat stronger. The cost of sulphate, due to a 
more expensive process of manufactiire, is somewhat more than 
that of sulphite pulp. 

2. POSSIBLE BASES OF DIFFERENTIATION 

Commenting on the problem, C. \V. Schwalbe stated' in 191 4 
that there was no simple method known at that time for distin- 
guishing between unbleached sulphite and sulphate pulps; also, 
that it is difficult to develop such a method because the pulps are 
so closely related. Schwalbe recognized, too, as do others who 
have made a study of the two pulps, that there are two differences 
between them which may be used as a basis on which to develop 
reactions which will differentiate them, namely, (i) the difference 
in the amounts of incrusting or Ugneous material, and (2) the dif- 
ferent chemical changes which have been brought about by the 
different digesting processes. 

1 Testing Methods for Sulphite and Sulphate Cellulose in Paper. Pulp and Paper Magazine, p. 21; Jan. 
1. 1914- 



6 Technologic Papers of the Bureau of Standards 

3. DIFFERENT AFFINITIES OF PULPS FOR DYES 

It is pretty generally known by persons who have made any 
analytic study at all of paper-making pulps that those pulps differ- 
ing in the degree of cooking, or of bleaching, or both, usually have 
quite different affinities for various dyes and stains. The dye 
most generally used to show the properties of different pulps in 
tliis respect is malachite green, a basic aniHne or coal-tar dye 
which has a great affinity for highly lignified fibers and very little 
or no affinity for pulps and fibers freed from incrusting matter. 
The result of this property is that, when malachite green alone is 
used to stain a pulp composed of a mixture of fibers having a high 
content of lignin and of other fibers more thoroughly digested, one 
gets a range of shades varying from deep green to very light green, 
or, perhaps, to the entire absence of color in the case of fibers that 
are completely freed from incrusting matter. Although there may 
be no sharp color line of demarcation to set off any one group of 
fibers against any other, results of this kind may serve the purpose 
of determining the thoroughness or the uniformity of the cooking 
or of the bleaching action. But if this or a similar dye or stain 
is followed by one of a contrasting color, as recommended by 
Siebert and Minor,- it will sometimes be found possible to separate 
quite distinctly a mixture of two different pulps, as, for example, 
a well-cooked from a slightly-cooked pulp, or a well-bleached from 
a poorly-bleached pulp, or a chemical from a mechanical pulp. 
These authors, however, recommend that malachite green be 
followed by an acid dye, while in the method described below both 
of the dyes used are basic. 

Whether the different affinities of the two pulps for various dyes 
and stains are due to different chemical properties of the pulps 
brought about by the different cooking methods, or whether they 
are due merely to the different amounts of incrusting matter 
remaining in the sulphite and sulphate pulps, is a question on 
which cellulose chemists do not agree. 

III. METHODS PROPOSED BY EARLIER EXPERIMENTERS 

In studying tliis problem the available methods proposed from 
time to time by others who have experimented along tliis Une were 
tried. Below is given a description of each method, together with 
a brief statement of results obtained by the writers in trying the 
method. 

^ The Differentiation of Sulphite Pulps, Paper, 25, No. 21; Jan. 2S, 1920. 



Differentiating Unbleached Sulphite and Sulphite Pulps 7 
1. KXEMM'S METHODS 

Klemm is given credit for developing two methods, in one of 
which use is made of malachite green alone, and in the other use 
is made of both malachite green and rosaniline sulphate. 

Klemm's malachite green method is described by R. W. 
Fannon ' as follows : 

The reagent consists of a saturated solution of malachite green, a coal-tar dye, to 
which 2 per cent acetic acid has been added. A portion of pulp is treated with a few 
drops of the reagent sufficient to soak it, and the excess blotted up. The fiber is then 
examined microscopically. Unbleached sulphite is colored full green; sulphate is 
colored light green. 

The results obtained by using tliis method were not satisfactory, 
since there is no sharp or distinct line of demarcation between 
the two pulps, some of the more deeply colored sulphate fibers 
showing a deeper green than some of the lighter colored sulphite 
fibers. These results are in harmony with the statements made 
above regarding the use of malachite green in staining various 
pulps and fibers. 

Schwalbe mentions another procedure,* a malachite green 
and rosaniline-sulphate method, wliich he also calls Klemm's 
method. No details as to making up the dye solutions or method 
of applying them are given. 

It was found, however, that a fairly good differentiation between 
the two pulps is had if they are stained for about two minutes with 
a one-half per cent aqueous solution of malachite green, rinsed 
with water, then stained \\-ith a solution of rosaniline sulphate 
acidified with sulphuric acid. The same results may also be 
obtained if these two stains are compounded in the right pro- 
portions before being applied to the pulps. 

When the chemical composition of rosaniline sulphate is com- 
pared with that of magenta, or fuchsine, one of the dyes recom- 
mended below, it is evident that they are very closely related, 
and that the color radical is the same in both. An insight into 
the constitution of these compounds may be had from any good 
treatise on organic chemistry. 

Pararosaniline and rosaniline ^ are the bases of the fuchsine 
dyes. Both are triacid bases, stronger than ammonia. The 
basic fuchsine or magenta dyes are formed by treating these 
bases with various acids, particularly hydrochloric and acetic, 

* An effort to find a simple means of differentiation between sulphite and sulphate pulp. (.\ thesis 
prepared at the University of Maine. June. 1916.) 

* Pulp and Paper Magazine, p. 2i;Jan. 1. 1914. 

^ A. Bemthsen. Organic Cheinistr>*. translation by J. J. Sudborough; New York. 1912. 



Technologic Papers of the Bureau of Standards 



water being eliminated during the reaction. The formula of 
rosaniline is 

<CeH,.NH3 
CeH^.NH^ or C,„H,iN30. 

C,H3(CH3).NH3 



By treating with hydrochloric acid, the following reaction 
takes place: 

CjoHjiNjO + HCl = C2oH3„N3Cl + HjO. 

Rosaniline Hydro- Rosaniline Water 

chloric hydrochloride 

acid 

From analogy, it appears that a similar reaction takes place 
when rosaniline is treated with sulphuric acid, and that rosaniline 
sulphate is essentially a basic fuchsine or magenta dye, but \\4th 
an add radical not usually found in dyes put out under this name. 

(QoH^iNjO)^ + H,S04 = (CoH,„N,),SO, + 2H,0. 

Rosaniline Sulphuric Rosaniline sul- Vater 

acid phate 

As the coloring power, however, of these dyes lies wholly in the 
basic constituent, there can be no doubt but that rosaniline 
sulphate is essentially basic fuchsine or magenta. 

One authority " states that basic magenta is a mixtiu-e of the 
hydrochloride and acetate of rosaniline and pararosaniline ; 
according to another, it is a mixture of the hydrochlorides of 
rosaniline and pararosaniHne. The formula of pararosaniline is 

<CeH,.NH3 1 
CeH^.NH,. or C^H.^NjO. 
CaH,.NH, j 

The reaction of this base with acids is like that of rosaniline. 

The malachite-green and rosaniline-sulphate stain, however, 
does not give as brilliant color contrast between the two kinds of 
fibers. This advantage of the use of basic fuchsine over that of 
rosaniline sulphate is probably explained by the greater solubility 
of basic magenta as compared "with that of rosaniline sulphate, 
since it was found by test that basic magenta is much more soluble 
in water than is rosaniHne sulphate. Tliis fact is in harmony with 
the known properties of the salts of these acids. 

fl Thomas H. Norton artifical dyestuifs used in the United States, Special Asent Series. No. 121. Bureau 
Foreign and Domestic Commerce. Washington D. C. Ira Remsen. Organic Chemistry. Fifth revision; 
New York, 1909. 



Differentiating Unbleached Sulphite and Sulphite Pulps 9 
2. SCHWALBE'S METHODS 

Schwalbe also describes ' two methods of analysis, in one of 
which aqueous solutions of ferric chloride and potassium ferro- 
cyanide are used, and in the other solutions of a copper salt and 
an organic dye. The former method is also briefly outlined by 
Fannon." 

The ferric-chloride and potassium-ferrocyanide method consists 
in extracting the pulps for about 30 minutes in alcohol and ether 
to remove rosin, treating with a 0.05 A'^ solution of ferric chloride 
at from 60 to 80° C for about 30 minutes, or until all the fibers 
settle to the bottom of the container, washing with distilled water, 
and treating with a i per cent solution of sulphuric acid, to wliich 
is then added from four to eight drops of a 2 per cent solution 
of potassium ferrocyanide. The container and contents are then 
placed on a water bath and kept at a temperature of from 60 to 
80° C for from 5 to 10 minutes. The pulps are then washed and 
examined under the microscope. Sulphite fibers are colored a 
deep blue, and sulphate fibers a much lighter blue. 

This method did not give results that would enable a distinction 
to be made in all cases between the two pulps, nor to permit 
estimations in any case. Moreover, the process is too long and 
tedious to be practical. However, since Schwalbe so liighly 
recommends this method, it is thought probable that better 
results could be obtained if enough time should be spent in study- 
ing and experimenting with it. 

By the copper method the pulps are boiled in a solution of a 
copper salt such as copper sulphate, washed, then treated with a 
solution of an organic dye such as benzopurpurine loB. The 
benzopurpurine treatment develops in some classes of fibers an 
intensely blue color, according to Schwalbe, due to the formation 
of a so-called copper lake with the copper salt retained by the 
fibers. 

This method was not experimented with, since Schwalbe liimself 
condemns it as being too involved and uncertain in results, 
especially with pulps so similar in their properties as unbleached 
sulphite and sulphate. 

T Pulp and Paper Magazine, i). 21; Jan. i, 1914. 
^ Thesis referred to above. 

34392°— 21 2 



lo Technologic Papers of the Bureau of Standards 

3. FANNON'S METHODS 

Fannon " found that a saturated aqueous solution of rosaniline 
sulphate, to which is added i to 3 per cent of alcohol and enough 
sulhpuric add to cause the solution to take on a violet shade, is 
a satisfactory stain. He used two methods of applying this 
stain and examining its staining action : 

In the first method, two or three drops of the solution were 
allowed to fall in the same spot onto the samples of sulphite and 
sulphate pulps tested, and the color reactions observed \vith the 
unaided eye. The unbleached sulphite pulps showed "a deep 
bluish center with a yellow ring siurounding," while the sulphate 
sample gave "a deep red coloration." "From 7 to 15 minutes 
after the stain was dropped on, the distinctive colorings were 
evident. After an hour or so the colors faded." 

In the second method, " mixtures of sulphate fibers and sulpliite 
fibers were made, stained with the last-named solution. The 
different fibers developed their respective colorations, and under 
the microscope estimations of each were possible." 

This stain was not found satisfactory when used according to 
either method recommended, because the color differences shown 
by the two pulps are not sharp enough to enable one to detect 
without doubt even the presence of small percentages of one pulp 
when mixed with the other. 

IV. THE MALACHITE-GREEN AND FUCHSINE METHOD 
1. SOURCES OF MATERIALS USED 

The samples of pulps and papers used in this investigation 
consisted of 188 pieces collected from a number of different firms, 
and represent pulps manufactured in all parts of this cormtry, 
and in at least four foreign countries, Canada, Finland, Norway, 
and Sweden. All possible information was obtained regarding 
these samples, such as the kind of wood used and in what locaUty 
grown, the degree of cooking, etc. 

The dyes and stains used during the earlier part of this investi- 
gation were obtained chiefly from the chemical di\dsion of this 
Bureau. Most of them had been in stock for some time, and all, 
or nearly all, were of German manufacture. But after the 
method given below had been pretty thoroughly worked out, 
samples of the two dyes used in this method were obtained from 
different sources in this country in order to determine whether 
the different makes of dyes were equally suitable for the purpose. 

^ Thesis rderred to above. 



V 



Differentiating Unbleached Sulphite afid Sulphite Pulps 1 1 
2. METHOD OF ATTACK AND EARLIER EXPERIMENTS 

The method of conducting the investigation was to try out 
on the two kinds of pulps the reaction of various biological stains 
and dyes recommended by authorities on microscopical methods, 
and also other stains and dyes that were suggested in one way or 
another. Most of the experimenting was carried on with red, 
green, and blue dyes, since dyes of these colors are usually the 
most brilliant and positive in their coloring action. The few 
yellow dyes that were tried did not give sufficiently brilliant 
color effects on the fibers, and little work was done \vith them. 

In making tliis investigation by what may be properly called 
the empirical method, a great number of tests were necessarily 
made that are relatively valueless and therefore are omitted 
from this publication. Those which may be of value to others 
who are experimenting along the same line are given in Table i . 

TABLE 1. — Interesting Experiments Made and Stains Used with the Color Reactions 

on Sulphate and Sulphite Fibers 

[Ext. alc.= extracted with alcohol; aq.=> aqueous; so'.= soIutlon.] 

How stained 



Satranin in equal parts water and alcohol, 
rinsed with water, Delafield's hema- 
toxylin. 

Ext. ale. boiled 1 minute. ^4 per cent aq. 
sol. malachite green, rinsed with water, 
rosanjline sulphate and little sulphuric 
acid. 

Ext. ale, boiled 1 minute. }.i per cent aq. 
sol. malachite green, rinsed with water, 
eosin in equal parts alcohol and water. 

Ext. ale, heated to 100°C in }'i per cent aq. 
sol. malachite green, rinsed with water, 
1 per cent aq. ale. sot. safranin. 

Boiled 1 minute in 1 part rosaniline sul- 
phate sol., then 1 part 1 per cent aq. sol. 
malachite green added, lightly rinsed 
with water. 

Ext. ale, boiled in water, acidified solu- 
tion 50 per cent alcohol, Deiafield s 
hematoxylin 10 to IS minutes, rinsed 
with water, J 2 P" cent sol. congo red 1 
minute, rinsed with water. 
; Ext. ale. boiled in water, acidified solu- 
tion 5U per cent alcohol, Delafield's 
hematoxylin left on until air dry, rinsed 
with water, ^2 per cent sol. congo red I 
minute, rinsed with water. 



Colorless te faint 

reddish 

brown. 
Clear blue, 

bundles 

green. 

Dark blue 



Light to dark 



Pink to light 
magenta. 



Color difierence 
quite noticeable. 



Pale gray to Differen t ia t i 
lavender. good. 



Colorless to 

faint purple. 



Light to dark 
red. 



Pits of sulphite 
fibers colored 
green. 

Do. 



Purple Good differentia- 
tion. 



Fair difierentia- 

tion. 



Purple with 
litUe red. 



Technologic Papers of the Bureau of Standards 



TABLE 1. — Interesting Experiments Made and Stains Used with the Color Reactions 
on Sulphate and Sulphite Fibers — Continued 







Action 


on— 




Serial 


How stained 






Remarks 


No. 










Sulphate 


Sulphite 




57 


Ext. ale, washed with 1 per cent aq. sol. 
tannic acid, then equal parts 1 per cent 


Blue 


Purple 


Good differentia- 






tion. 




aq. solutions acid ftrchsine and malachite 










green 3 minutes, rinsed with water. 








79 


Ext. ale, boiled in water, dried with filter 
paper on slide, then 50 parts each o( 1 per 
cent aq. solutions magenta and malachite 
green and 1 part 1 per cent aq. sol. tannic 
acid 2 minutes, quickly rinsed in 50-50 
aq. ale. sol. slightly acidified with HCl, 
rinsed with water. 


Greenish blue.. 




Differentiation ex- 
cellent. 


82 


Boiled in water, i 2 per cent aq. sol. mala- 


Blue 


do 


Color difference not 




chite green and aq. sol. rosaniline sul- 






as decisive as 




phate and little HsSO,, all left on fibers 






when magenta is 




2 mhiutes, then rinsed with water. 






used in place of 
rosaniline s u 1 - 
phate. 


84 


Slide as made up by No. 79 examined under 


Various colors . 


Various colors. 


No distinguishing 


1 microscope in polarized light, wiUi both 






properties 


parallel and crossed nicols. 






appeared. 


85 Boiled In water, pulped and examined 


Yellow, orange. 


Yellow, orange, 


Do. 


under microscope in polarized light with 


and blue. 


and blue. 






both parallel and crossed nicols. 









Some of the pulps were extracted with alcohol to remove 
resins, and this fact is indicated in each case in the table. The 
pulps were then rinsed and cooked, at first, in clear water, and 
pulped, no chemical being used in the cooking process, as it was 
thought that any chemical treatment might possibly interfere 
with the staining action to follow. Experiments that were con- 
ducted later, however, indicated that cooking the sample of 
paper in a one-half per cent aqueous solution of caustic soda 
does not have any effect on the action of the dyes. The alcohol 
used at various times and for various pvu-poses, as indicated, 
was in all cases ethyl alcohol. The color appearances and other 
characteristics noted are those which appeared under the micro- 
scope. 

3. DETAILED METHOD OF USING 

The stain which was found to be most satisfactory in diflfer- 
entiating between unbleached sulphite and sulphate pulps or 
fibers was a mixture of one part of a 2 per cent aqueous solution of 
malachite green and two parts of a i per cent aqueous solution of 



Differentiating Unbleached Sulphite and Sulphite Pulps 13 

basic fuchsine, or magenta. The solutions were made up accord- 
ing to the following formulas, kept in tightly stoppered separate 
bottles, and mixed only when wanted for use : 

A — Malachite green 2 g 

Distilled water .;:.... 100 cm* 

B — Basic fuchsine i g 

Distilled water 100 cm ^ 

Since there is considerable variation in the quality of dyes from 
various sources, it is not to be expected that any given combina- 
tion of dyes or method of procedure will best fit all cases; it is, 
indeed, more than probable that the compovmd stain will have to 
be modified somewhat as to its two components, depending on the 
source of the dyes. 

After this stain, therefore, has been made up according to 
formula, it will be necessary to test it out on samples of sulphite 
and sulphate fibers. To do this, samples of unbleached sulphite 
and sulphate pulps should be prepared and a few fibers of each 
placed on a slide, care being taken not to get the two samples 
mixed. The fibers are then dried and stained, as directed below, 
and then examined under the microscope. All the sulphate fibers 
should have a blue or blue-green color, and all the sulphite fibers 
should have a purple or lavender color. If any purple fibers 
appear in the sulphate pulp this indicates that too much fuchsine 
is present in the combination, and a little more malachite green 
solution must be added to coimteract this effect. If, on the other 
hand, some of the sulphite fibers show green or blue, there is too 
much malachite green in the combination, and more fuchsine 
solution must be added. Of course the analyst must be sure that 
he is using authentic samples of the two pulps for this test. When 
tested out in this manner and the proper combination found, the 
stain is ready to be used on unknown combinations of fibers con- 
taining either imbleached sulphite or sulphate, or both. 

A mixture of one-haif sulpliite and one-half sulphate may also 
be used to test out the stain, the proper combination for the stain 
being indicated when one-half of the fibers are colored blue, and 
the other half purple. 

The stain should not be used for more than a few hours after 
being compounded and should be made up anew at least each 
day. 



14 Technologic Papers of the Bureau of Standards 

The method of preparing the samples of pulps or papers for 
staining, and of applying the stain, is as follows: 

The sample is boiled for a few minutes in water or in a one- 
half per cent aqueous solution of sodium hydroxide, and the fibers 
are thoroughly disintegrated by shaking in a test tube or other 
receptacle about half filled with water, glass beads being added 
if the fibers can not otherwise be separated. Several fibers are 
then removed by means of a teasing needle, or preferably by 
means of a glass tube " about seven thirty-seconds of an inch in 
diameter, placed on a microscope slide, and dried by the use 
of hard filter or blotting paper. Two or three drops of the com- 
pound stain are then placed on the fibers by means of a suitable 
dropper or a pipette and allowed to remain 2 minutes, during 
which time the fibers are being teased apart and moved about in 
the stain on the slide. This teasing is necessary in order that 
the stain may have equal opportunity to act on all the fibers. 
At the end of 2 minutes the excess stain is removed with three 
or four thicknesses of hard filter paper, and the fibers treated with 
three or four drops of a weak aqueous solution of hydrochloric 
add, made by adding i cm' of concentrated acid (sp. gr. 1.19; 
HCl 37 per cent) to i liter of distilled water. The acid solution 
is allowed to remain on the slide for from 10 to 30 seconds, during 
which time the fibers are teased and moved about rapidly. Fol- 
lowing this, the excess acid solution is removed with filter paper, 
three or four drops of distilled water applied, the fibers quickly 
teased about, and the water absorbed with filter paper. If all the 
excess stain has been removed from the sHde at this point, a drop 
or two of water may be added, the fibers spread about on the slide, 
and a cover glass placed over them. But if too much stain 
remains on the slide at this point, it will be necessary to rinse 
again wth distilled water before applying the cover glass. After 
the cover glass has been placed in position the fibers are ready for 
examination imder the microscope. 

4. ESTIMATING PERCENTAGES 

The color contrast not only enables one to detect the presence 
of one or both of these fibers, but is sharp enough to enable one, 
after some practice, to make an approximately correct estimate 
of the percentages of each of these fibers present. 

"> F. C. Clark, Paper Testing Methods, Tappi Publishing Corp., New York. N, Y.; 1920. 



Differentiating Unbleached Sulphite and Sulphite Pulps 15 

In order to get a practical idea as to what could be accomplished 
in estimating the percentages of sulphite and sulphate fibers when 
stained as directed, three persons, all of whom had had experience 
in estimating the percentages of fibers stained with the zinc- 
chloride and iodine stain, made a number of estimations on known 
mixtures of these two pulps. 

Seven mixtures, made from representative samples of sulpliite 
and sulphate pulps, were prepared by weighing on a chemical 
balance the proper proportions of each pulp, the weights of the 
two components totaling 30 g in each case. The pulps were then 
thoroughly mixed by agitating in a tight container with consid- 
erable water. The series made up contained 20, 25, 40, 50, 60, 
75, and 80 per cent of unbleached sulphite. A representative 
portion of each member of this series was placed in a container 
and labeled. Microscope slides were then made up from each 
of the seven samples, each slide being given an unknown mark 
of identification, and handed over to the analysts for their esti- 
mations. Four different series of estimates were made, in each 
of which a different make of American dyes was used. 



V. SUMMARY OF RESULTS 

In the tables below are given the results of estimates on the 
seven fiber mixtures, each table showing the results obtained by 
using dyes from one of the four sources. 

TABLE 2. — Results of Analyses, Using Dyes from First Source 





Ob- 
server 


Percentage sulphite in mixture 


Error 

o( 
aver- 
age 


Prob- 
able 
error 

<r) 




Number of 
estimations 


Estimated 


Actual 


Huge 
error 

(u) 




Maxi- 
mum 


Mini- 


Aver- 
age 


16 


A 

C 
A 
C 
A 

C 
A 
C 
A 
C 
A 
C 
A 
C 


40 
50 
50 
50 
60 
90 
75 
80 
80 
90 
90 
80 
95 
90 


20 
10 
20 
20 
25 
25 
40 
40 
60 
60 
25 
40 
75 
25 


23.8 
27.9 
33.1 
33.9 
41.6 
50.7 
51.6 
57.1 
67.2 
69.6 
73.7 
72.9 

80.6 
76.4 


20 
20 
25 
25 
40 
40 
50 
50 
60 
60 
75 
75 
80 
80 


Per cent 

+3.8 
+ 7.9 
+8.1 
+8.9 

+ 1.6 
+ 10.7 

+ 1.6 
+ 7.1 
+ 7.2 
+ 9.6 
-1.3 
-2.1 
+0.6 
-3.6 


Per cent 
5. 1 
8.8 
8.2 

8.7 
7.1 

12.7 
5.4 
9.5 
7.1 
8.7 
9.6 
7.8 
3.4 

10.1 


Per cent 

12.3 




21.6 


16.. . 


20.0 




21.2 


16 


17.3 




30.9 


16 


13.2 




23.1 


16 


17.3 




21.2 


16 . . .. 


23.4 




18.9 




8.2 




24.7 







1 6 Technologic Papers of the Bureau of Standards 

TABLE 3. — Results of Analyses, Using Dyes £rom Second Source 





Ob- 
server 


Percentage sulphite in mixture 


Error 

ol 
aver- 
age 


Prob- 
able 
error 

(r) 




Number ol 
estimations 


Estimated 


Actual 


Huge 
error 

(u) 




Maii- 


Mini- 


Aver- 
age 


16 


A 

B 
C 
A 
B 
C 
A 
B 
C 
A 
B 
C 
A 
B 
C 
A 
B 
C 
A 
B 
C 


40 
25 
40 
50 
40 
25 
75 
60 
75 

75 
60 
60 
80 
75 
60 
80 
80 
80 
80 
80 
80 


20 
25 
20 

20 
25 
20 
25 
50 
30 
50 
60 
40 
50 
50 
50 
60 
80 
70 
75 
75 
70 


24.7 
25.0 
24.0 
37.2 
35.0 
24.0 
50.0 
53.3 
47.5 
54.1 
60.0 
51.7 
65.0 
66.7 
56.0 

75.6 
80.0 
77.0 

78.4 
78.3 
73.7 


20 
20 
20 

25 
25 
25 
40 
40 
40 
50 
50 
50 
60 
60 
60 
75 
75 
75 
80 
80 
80 


Per cent 

+4.7 
+5.0 
+4.0 

+ 12.2 
+ 10.0 
-1.0 
+ 10.0 
+ 13.3 
+ 7.5 
+4.1 
+ 10.0 
+1.7 
+5.0 
+6.7 
-4.0 
+0.6 
+5.0 
+ 2.0 

-1.6 
-1.7 
-6.3 


Per cent 
6.0 
3.4 
6.0 

10.0 
8.3 
1.5 

10.5 
9.5 

10.8 
5.4 
6.7 
6.2 
7.6 
9.1 
4.3 
4.3 
3.4 
3.0 
1.9 
2.0 
5.1 


Per cent 


2 




5 




16 




3 


20.2 


5 


16 




3 


23.3 

26.3 


e 


16 


3 




6 




16 


18.6 


3 


5 


10.4 


16 


3 


8.2 


5 


16 




3 




4 









TABLE 4. — Results of Analyses, Using Dyes from Third Source 





Ob- 
server 


Percentage sulphite In mixture 


Error 

ol 
aver- 
age 


Prob- 
able 
error 

(r) 




Number of 
estimations 


Estimated 


Actual 


Hugo 
error 
(u) 




Maxi- 
mum 


Mini- 
mum 


Aver- 
age 


16 


A 
B 

A 
B 
A 
B 
A 
B 

A 
B 

A 
B 
A 
B 


50 
40 
75 
50 
60 
75 
60 
75 
75 
80 
80 
80 
80 
80 


20 
20 

20 
20 
25 
25 
20 
40 
25 
40 
60 
50 
50 
70 


27.5 
26.9 
32.5 
37.2 
43.1 
48.4 
45.3 
55.3 
55.0 
63.8 
74.4 
70.9 

75.3 
78.4 


20 
20 
25 
25 
40 
40 
50 
50 
60 
60 
75 
75 
80 
80 


Per cent 

+ 7.5 
+ 6.9 
+ 7.5 
+12.2 
+ 3.1 
+ 8.4 

- 4.7 
+ 5.3 

- 5.0 
+ 3.8 

- 0.6 

- 4.1 

- 4.7 

- 1.6 


Per cent 

8.8 
7.1 
10.6 
11.0 
8.0 
9.9 
8.1 
7.6 
8.0 
8.1 
4.9 
6.3 
6.4 
2.2 


Per cent 


16 / 


17.2 


16 


16 




16 




16 




16 




16 




16 




16 




16 




16 




16 


15.5 


16. . . . 









Differentiating Unbleached Stdphite and Sulphite Pulps 1 7 
TABLE 5. — Results of Analyses, Using Dyes from Foiuth Source 





Percentage sulphite in mixture 


Error 

of 
aver- 
age 


Prob- 
able 
error 

(r) 


Ob- 
server 


Estimated 


Actual 




Maxi- 
mum 


Mlni- 


Aver- 
age 


A 

B 


25 
25 


20 
20 


20.6 
20.6 


20 
20 


Per cent 

-1-0.5 
+0.6 


Per cent 

1.2 
1.2 


A 
B 


40 
50 


20 
20 


28.2 
27.1 


25 
25 


-1-3.2 
+2.1- 


5.0 
4.8 


A 

B 


60 
50 


25 
25 


40.6 
39.7 


40 
40 


-HO. 6 
-0.3 


5.3 
3.0 


A 
B 


60 
75 


10 
40 


48.8 
50.9 


50 
50 


-1.2 
-fO.9 


3.3 
5.5 


A 
B 


75 
75 


25 
50 


58.8 
59.4 


60 
60 


-1.2 
—0.6 


7.7 
4.8 


A 
B 


80 
80 


60 
60 


74.1 
74.1 


75 
75 


—0.9 
—0.9 


4.7 
4.7 


A 

B 


80 
80 


75 
75 


78.2 
78.5 


80 
80 


-l.B 
—1.5 


2.0 
1.8 



Huge 
error 

(u) 



The analysts, or persons who made the estimations, are referred 
to as "A," "B," and "C." 

The error of averages is the difference between the average of all 
estimations for that particular case and the actual percentage of 
sulphite in the mixture. The average result is computed from a 
number of estimations in most cases ; the exact number of estima- 
tions in each case is given in the tables. 

The most probable error is an error of such magnitude that a 
single estimation has an equal chance of being either within the 
error or outside of it. The given errors are computed by the 
method of least squares according to the formula 






r = 0.6745 



in which r is the most probable error, K is the error of one estima- 
tion, 2X- is the sum of the squares of all errors of n estimations, 
and n is the total number of estimations made on that particular 
mixture by the given analyst. 

The huge error is an error of such magnitude that the chances are 
equal that 9 estimations out of 10 will be within the error, and 
only I in 10 greater than it. These results are computed by the 
method of least squares, according to the formula 



1.65 






or M = 2.44r, 



in which u is the huge error. 



l8 Technologic Papers of the Bureau of Standards 

In no case did an individual analyst make more than one estima- 
tion on the same miscroscope slide or the same field of fibers. 

It is noteworthy that the errors in the last series, or table, are 
much less than those in the first three series. This is no doubt due 
in large part to the differences between the dyes used in the first 
three series and those used in Table 5, since those used in the last 
series gave much more satisfactory' color effects than those used in 
the first three series. This result is also certainly due in part to the 
greater familiarity and experience the analysts had with the stain 
at the time the last series was run. 

There are at least two criticisms that may be offered against 
these estimations. The first is that the results given may not 
quite represent estimates on wholly unknown mixtures, since each 
analyst knew in what proportion each of the seven combinations 
in the series was made up; although, as stated above, each sample 
was marked in code so that the analyst could not know what com- 
bination was being examined. When a study of the individual 
estimates is made, it appears that this circumstance did have an 
appreciable influence on the estimates on the mixtures near either 
end of the series. But since o per cent and 100 per cent are limits 
in all mixtures, it seems probable that estimates on mixtures near 
these limits will always be more nearly correct than estimates on 
mixtures containing a higher percentage of the smaller constituent. 

The second criticism is that it is not practical in most cases to 
make 1 6 or 18 different estimates on the same sample of pulp or 
paper. This criticism is valid, especially as applied to mill condi- 
tions ; for the paper-mill chemist is usually too busy to give so much 
time to the study of one sample of pulp or paper. It is necessary, 
however, that anyone, whether novice or expert, doing work of tliis 
kind, shall become famiHar by actual experience with the use and 
properties of any stain before reliable results in estimating per- 
centages can be had. To get best results in estimating, it is also 
necessary that one keep constantly in practice, and refer often to 
standard or known mixtures, accurately made up, and kept always 
at hand. When the analyst becomes familiar with the character- 
istics and use of the stain described above, it is probable that esti- 
mates can be made by its use as quickly and with as much accu- 
racy as with the zinc-chloride and iodine stain. 

Washington, November 27, 1920. 



018 374 065 9 



He 



LIBRARY OF CONGRESS 

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018 374 065 9 • 



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